Medical care of individuals requires the widespread use of needles for taking blood samples, intravenous drug delivery, and the introduction or removal of other fluids via cannula, needles, or syringes. In the current context, the use of hypodermic needles to deliver plasma, anesthetics, or other medications has become commonplace in medicine, science, veterinary medicine, and biotechnology. The use of a hypodermic needle typically involves first inserting a needle into the patient, injecting a substance or withdrawing a substance as required, and then removing the needle from the patient. In most applications, the withdrawn and contaminated needle must be handled very carefully during disposal to avoid needle stick injury.
To help prevent health care workers from becoming injured, guards have been developed to block the tip of these needles after use. Indeed, needle stick protection for medical professionals has become of particular importance in recent years because of the prevalence of potentially fatal infectious diseases, such as, for example, Acquired Immune Deficiency Syndrome (AIDS) and hepatitis, that can be transmitted by the exchange of bodily fluids through inadvertent wounds caused by accidental needle tip pricks after withdrawal from infected patients. Accordingly, many kinds of needle protection devices are available for providing post injection needle stick protection.
Devices which have been introduced to provide added protection against punctures by used needles fall into three basic categories, those which hide the withdrawn needle within a needle shield launched via a needle shield launching mechanism, those which require placement of a separate needle guard, and those which include a sliding shield which must be manually pushed along the needle shaft and over the tip of the used needle. Most of these needle guards are cumbersome and interfere with a single-handed procedure, and or require additional complicated pieces to attach the needle guard to the needle tip.
Of the first type, i.e., devices which hide the withdrawn needle within a launched needle shield, there are several designs. However, all of these designs have undesirable features which make them unsuitable for many applications. For example, in one conventional design, a spring biased needle shield is provided which lockingly engages with the needle tip when the user manually activates the spring mechanism after the needle is withdrawn from the patient. However, while this mechanism provides for preventing the needle shield from disengaging and moving back down the length of the needle, the needle shields are only frictionally engaged to the tip of the needle, such that it is possible to slip the needle shield off of the distal end of the needle leaving the needle tip exposed. In addition, this design requires the user to manually activate the spring mechanism, which adds to the complexity of the design, manufacture, and use of the hypodermic needle assembly.
In another conventional design, the needle has a slightly expanded portion at the tip which prevents the needle shield from sliding off of the distal end of the needle once engaged. However, the needle shields utilizing this design still require the user to manually activate a second mechanism that then engages the needle guard, adding to the complexity of the design, manufacture and use of the hypodermic needle assembly.
Within this first category there are also a number of hypodermic needle assemblies for shielding the needle tip from being exposed once the needle is withdrawn from the patient which are automatically activated by the depression of the hypodermic plunger. However, the needle guards provided in most of these prior art designs consist of a simple hollow sleeve having an open distal end. While this design does provide protection from most inadvertent contact with the needle tip, it is still possible with such designs for a user to accidentally or purposefully insert a finger into the open distal end of the needle guard sleeve and thus come into contact with the contaminated needle tip.
Of the second and third types of needle shields, i.e., those which require placement of a separate needle guard or which use a shield that is manually pushed along a needle, there are several different designs. A number of these needle shields include either a spring-clip fitting or a frictional fitting, which are either placed directly on the tip of the needle or are movable from the base of the needle to the tip of the needle along the longitudinal direction of the needle. In the later embodiment, the user manually slides the needle shield toward the tip of the needle to thereby engage the needle shield around the needle tip. However, these manually activated designs require that the user either slide or apply the needle shield to the tip of the needle by hand, significantly raising the risk of unintentional contact with the needle tip.
Present day techniques thus offer a large number of solutions for protecting medical staff from used needles. However, as noted above, the known solutions suffer from at least one serious drawback. Accordingly, a hypodermic needle assembly is needed which reduces the risk of unintentional exposure of the used needle after use by automatically engaging the needle shield once injection is complete, without the need for additional complex mechanisms or cumbersome user operation.